1. Field of the Invention
The present invention relates to a damper circuit for a synchronous servo-motor.
2. Brief Discussion of the Related Art
In the field of aviation, servo-motors are used in systems for controlling flight control surfaces. Such servo-motors are generally used as actuators and dampers, but it is also possible to use them as dampers only. In the damper mode of operation, the movable element of the servo-motor is moved by an external force that generates electrical energy in the windings of the servo-motor, which energy is taken to damper resistors in order to be dissipated therein. The damping as produced in this way obeys a linear relationship of slope that depends directly on the resistance of the resistors.
It can nevertheless be understood that it would be desirable for damping to be greater when the movable element is moved suddenly and quickly.
That is why circuits have been devised that provide a damping relationship that is not linear. It is thus known to provide damping circuits that make use of electromechanical relays. Such relays give rise to problems of size, of weight, and of reliability. Furthermore, they need to be controlled by a control circuit that requires power.
It is also known to provide damper circuits that make use of a programmable logic circuit. Such programmable logic circuits are nevertheless complex and the risks of failure are relatively numerous, so it is very expensive for them to be certified for critical use in the operation of an airplane. In addition, it is preferable to use components that do not need a power supply in order to operate so that damping can be ensured even in the event of a failure of the power supply.
It might be thought that zener type diodes can be connected in series with the damper resistors in order to enable the damper resistors to be connected selectively. Nevertheless, such zener diodes deform the voltage waveform even though it is desirable to conserve a sinusoidal waveform both for the voltage and for the current. Furthermore, the conduction voltages of zener diodes are set by their manufacturers, thereby putting a limit on available values.